Overheating of bearing – emergency procedures

What should be done in case of overheating?

In case of overheating the outside shaft diameter is getting bigger. The most it increases, the less oil will be able to get in. Less oil – higher temperature and so on. One of the possible step (not suitable for all cases) to perform when a bearing is overheated more than 65% is o run the kiln on auxiliary motor until shaft temperature decrease below 50oC. After that the kiln operation should be restarted.

Analyzing bearing liner design very important is an oil used. But even the best oil cannot solve contact surface problems. Too low clearance between shaft and bearing cannot be replaced by good quality of synthetic or thick oil. Oil loses its viscosity very quickly.

Summarizing the overheating creating something like “chain of reasons and causes”:

Generally this method is quite dangerous on bearing because housing is open so the dust can get into component. Another point is that you never know what you are cooling exactly, shaft or housing? Always have thermal expansion on each component in mind.

Another and definitely the best method is to use oil re-circulation with cooling and filters (cleaning). Even small units are available on the market with fast installation.

If the existing problem is rather small you can try to run kiln using auxiliary drive (as mention above). The advantages of this method is time. Running the kiln slowly you are getting time to decrease shaft temperature, time to skip “chain of reasons and causes” and time to get back proper oil viscosity.

As a good auxiliary method commonly used is cooling the roller flank to limit shell heat transition to shaft by air or by water. Using the water is dangerous and should be used like the last possible step (very progressive application to avoid thermal shock. Also be aware to protect housing from water. Any heat shock can lead to spalling (on surface).

In case of emergency sometimes changes of oil is necessary. Oil with the highest viscosity possible should be used, assuming the real viscosity will drop because of temperature. Of course the synthetic I oil can be used as well but some data mast be checked. Before oil usage check if it can be mixed with mineral and also it does not chemically attack any bearing components.

Under no circumstances grease or molycot cannot be used. It can completely block the oil pocket.